In today's advancing semiconductor manufacturing industry, increased integration levels and decreased feature sizes mandate the use of highly accurate and precise semiconductor manufacturing equipment. When the manufacturing tool involves the movement of the semiconductor wafer before or during processing, the movement must be highly precise and accurate and free from vibration or other disturbances that can displace the semiconductor wafer and result in misalignment, poor feature resolution, or other anomalies or defects.
It is also of critical importance to manufacture as many semiconductor devices as possible within a given time period and similarly important to do so at a minimal cost. It is therefore quite advantageous to use semiconductor manufacturing tools that simultaneously process multiple semiconductor wafers thereby lowering production costs by increasing throughput through a given piece of equipment and decreasing cycle time. Many semiconductor manufacturing tools that simultaneously process multiple semiconductor wafers involve the simultaneous movement of the wafers as the wafers undergo processing. For example, in a photolithography tool such as a stepper, a semiconductor substrate is retained upon a stage that incrementally moves in steps with respect to an e-beam or other fixed exposure or direct writing system components. In an effort to simultaneously process multiple substrates in a semiconductor tool at the same time while maintaining the integrity of the movable parts such as the stages that retain wafers, conventional approaches include the examples shown in FIGS. 1 and 2.
FIG. 1 shows one prior art example of a processing tool subject to vibration or other disturbances in the motion of the stage that holds a semiconductor wafer. Moveable stage 3 includes surface 1 for retaining a semiconductor wafer 17 thereon. Base 7 may be formed of stone or may be another massive fixture coupled to the ground. Hardware 5 is fixedly coupled to base 7. Magnetic field 9 may be used to maintain spacing between stage 3 and the fixture consisting of base 7 and hardware 5 and enables stage 3 to move with respect to the fixture consisting of base 7 and hardware 5. Magnetic field 9 may be produced by a set of opposed magnets oriented to repel each other. When stage 3 moves, such as along direction 11 to the right, this movement effectuates a reactive force 15 exerted on the fixture of base 7 and hardware 5. The effect of this reactive force 15 is to cause disturbances and vibrations in the movement of stage 3 as it moves along direction 11. Surface 1 includes semiconductor wafer 17 thereon and semiconductor wafer 17 may undergo processing while being moved along direction 11. Various metrology or lithography operations may be performed upon semiconductor wafer 17 by fixed exposure components 13 as stage 3 is moved. The disturbances and vibrations produced as stage 3 moves along direction 11 adversely affect the positioning of semiconductor wafer 17 and produce various problems such as misalignment, inaccurate readings, and poor resolution of features formed on semiconductor wafer 17 such as due to poor or varying focus.
FIG. 2 shows another conventional approach with balance mass 25 interposed between fixed base 27 and stage 3. Various conventional methods may be used to force air 29 between balance mass 25 and base 27 to avoid solid contact between these two components and stage 3 is moveable over balance mass 25 due to magnetic repelling force 9. When stage 3 moves, such as along direction 21 to the right hand side, balance mass 25 moves along direction 31 which is opposite to direction 21, to counteract the movement of stage 3 and avoid vibration or other disturbances to the motion 21 of stage 3. This approach requires an additional suspended, moving part—balance mass 25 that must be delicately positioned and maintained between stage 3 and base 27. FIG. 2 is not shown to scale and a weight ratio of stage 3: balance mass 25, may be typically on the order of 1:100. In other words, balance mass 25 is massive, especially in processing equipment in which stage 3 accommodates semiconductor wafers 17 that may have diameters of 450 mm or greater. Fixed exposure components 13 may be used to perform a lithography operation on semiconductor wafer 17 while semiconductor wafer 17 and stage 3 are moving.
Conventional tools and methods therefore suffer the shortcomings of vibrations or other disturbances in the motion of the stage, the requirement to use a massive mass balance to counteract the motion of the stage, or both.
The present invention addresses these shortcomings.